Process for the preparation of methionine

ABSTRACT

The invention relates to a process for the preparation of methionine of high bulk density, in which a mixture which comprises a compound which has a foaming action and a compound which influences the crystallization is added to the hydrolysis solution, and to the mixture itself.

The invention relates to a process for the preparation of methionine ofhigh bulk density, in which a mixture which comprises a compound whichhas a foaming action and a compound which influences crystallization isadded to the hydrolysis solution, and to the mixture itself.

It is known that the preparation of amino acids is often associated withdifficulties. Handling of solutions or suspensions containing aminoacids already leads to severe foaming in laboratory processes, but aboveall of course in industrial production. This undesirable effect can leadnot only to the production proceeding in a very problematic manner andwith poor space/time yields, but in individual cases also to failure ofan economical production of the amino acid.

JP 09000241 thus describes that the addition of various additives fromthe family of nitrogen-containing polyoxyalkylenes in the fermentativeproduction of amino acids leads to a reduction in foaming. JP 09000241relates to the preparation of defoamer mixtures which are composed offats or oils and the reaction products of fatty acids or derivativesthereof and polyalcohols with alkylene oxides.

These mixtures are suitable for use in fermentations. It is known thatthe yield of lysine and tryptophan production can be increased ifsilicone are used as foam-destroying additives, instead of sunfloweroil. The influence of various silicone oils is investigated bycomparison in Khim.-Farm. Zh (1972), 6(5), 27-30.

In the carbonate process known from EP 0 780 370, methionine is obtainedon acidification of a solution of potassium methioninate with carbondioxide in accordance with the equation.

Methionine is in general precipitated out of these solutions in the formof very flat leaflets, separating off of which proceeds only very slowlyand therefore uneconomically.

There are therefore attempts to influence the crystallization propertiesof the methionine by addition of particular auxiliary substances.

It is demonstrated in JP-11-158140 that the use of various auxiliarysubstances, such as hydroxymethylpropylcellulose, sorbitan monolaurateor polyvinyl alcohols, influences the crystal habit, and the bulkdensity of the methionine obtained in this way increases.

These compounds are added in an amount of at least 500 ppm during thecrystallization, which is carried out continuously and proceeds in twostages under specific stirring conditions. A round-particled methionineis obtained.

No additive or mixture of additives with the aid of which at the sametime the foam which forms in the various stages of methioninepreparation can be suppressed and the crystal habit of the methioninewhich has precipitated out, in particular in the carbonate process, canbe improved is known from the prior art.

The present invention is based on the object of minimizing the formationof foam in the methionine process and at the same time positivelyinfluencing the crystal habit of the methionine which has precipitatedout after the recrystallization.

The invention provides an aqueous mixture which comprises compounds ofthe general formula (additive (1))C_(n)H_(2n+x)C═O—O—[CH₂—CH₂—O]_(m)—H  (1),

-   -   in which the symbols denote:    -   n: an integer from 9 to 19, preferably 15 to 17,    -   m: a distribution in the range from 1 to 10, wherein the maximum        is preferably 5 to 8, in particular 6 to 7,    -   x: 1, −1, −3, −5, wherein 2n+x is not less than 1,        and additives (2) from the group consisting of modified        celluloses, in particular methylcellulose,        methylhydroxycellulose, methylhydroxypropylcellulose,        hydroxypropylcellulose, hydroxyethylcellulose, sodium        carboxymethylcellulose, sodium        carboxymethylhydroxyethylcellulose and sodium        carboxymethylhydroxypropylcellulose in a weight ratio of 1:10 to        10:1, preferably 1:3 to 3:1.

The fatty acid contents in compounds according to formula (1) arepreferably of natural origin, and are saturated or unsaturated,depending on the meaning of x.

The mixture is advantageously employed in the form of an aqueoussolution or emulsion with a total additive content of 1 to 5 wt. %, inparticular 2 to 4 wt. %, based on the total amount.

In order to produce a stable emulsion, it is merely necessary to treatthe mixture with a conventional blade stirrer. Since hydroxycellulosesdissolved in water can lead to highly viscous solutions, it isadvantageous to use low molecular weight hydroxycelluloses with aviscosity of <300 mPas (as a 2% solution in water). The viscosity canfurthermore also be adjusted via the degree of dilution.

Preferably, an aqueous solution or emulsion of the additives (1) and (2)with a viscosity of between 5 and 5000 mPas, based on a 2% solution ofthe additives in water, in particular 10 to 500 mPas, is prepared bydissolving or emulsifying the compounds according formula (1) and (2) inthe desired amount.

It has been found that the mixture described is suitable for reducingthe foaming in process solutions obtained during the preparation ofmethionine and at the same time effecting the formation of largercrystals during the recrystallization.

One important aspect of the invention is that the defoaming action andthe crystallization can be controlled by changing the ratios of amountsof (1) to (2) in the mixture.

Foaming depends greatly on the composition of the process solutions andthe other process conditions, such as, for example, pressure andtemperature.

The mixtures according to the invention already display their defoamingand a crystal growth-promoting action when small amounts are added.Amounts of 10 to 500 ppm, based on the methionine, are already active.

At the same time, it is to be found that the compounds (1) and (2)employed according to the invention have no adverse influence on theaction of the other particular compounds.

On the contrary, it is the case that the interaction of (1) and (2) canlead to an improvement in the crystal structure (see, for example, imageno. 1703045).

The invention also provides a process for the preparation of methionine,in particular with a purity of 80 to 100 wt. %, by reaction of thecomponents 3-methylmercaptopropionaldehyde, hydrogen cyanide, ammoniaand carbon dioxide or of those components from which the above-mentionedcomponents can be prepared, optionally in the presence of water, to give5-(2-methylmercaptoethyl)-hydantoin and conversion thereof intomethionine, which is characterized in that, before carbon dioxide ispassed in, an aqueous mixture which comprises compounds of the generalformulaC_(n)H_(2n+x)C═O—O—[CH₂—CH₂—O]_(m)—H  (1),

-   -   in which the symbols denote:    -   n: an integer from 9 to 19, preferably 15, 17 or 19,    -   m: a distribution in the range from 1 to 10, wherein the maximum        is preferably 5 to 8, in particular 6 to 7,    -   x: 1, −1, −3, −5, wherein 2n+x is not less than 1,        and additives (2) from the group consisting of modified        celluloses, in particular methylcellulose,        methylhydroxycellulose, methylhydroxypropylcellulose,        hydroxypropylcellulose, hydroxyethylcellulose, sodium        carboxymethylcellulose, sodium        carboxymethylhydroxyethylcellulose and sodium        carboxymethylhydroxypropylcellulose, is added to the hydrolysis        solution obtained from 5-(2-methylmercaptoethyl)-hydantoin in a        weight ratio of 1:10 to 10:1, preferably 1:3 to 3:1, in a total        amount of 5 to 5000 ppm, preferably 5 to 500 ppm, based on the        methionine (wt. %) contained in the solution, and the methionine        which has precipitated out is dissolved and, in particular using        the mother liquor, which preferably comprises the additives (1)        and (2) mentioned, is crystallized in the presence of        crystalline methionine, optionally with the addition of further        amounts of the aqueous mixture.

According to the invention, the high stirring energy known from theprior art does not have to be introduced during the precipitation or thecrystallization. The same applies to the CO₂ pressures known from theprior art. Only a uniform distribution of the carbon dioxide, which hasbeen introduced, during the precipitation of the methionine into thehydrolysis solution remains essential.

The process claimed can be carried out continuously or discontinuously.

During the precipitation of the methionine, with the addition of carbondioxide, from the solution obtained as the hydrolysis product, theadditive (1) has a defoaming action, while at the same time the presenceof (2) has no adverse influence on the defoaming.

The recrystallization is preferably carried out by a procedure in which,preferably, methionine suspended in the mother liquor is pumped incirculation at a temperature of 30 to 60° C., and a methionine solutionwhich has a concentration of 70 to 150 g/l, in particular 90 to 130 g/l,and has been heated up to 60 to 110° C., in particular 80 to 100° C., isadmixed to this suspension. The methionine solution mentioned lastoptionally comprises a content of 5 to 20 vol. % of mother liquor fromthe preparation process.

Methionine precipitates out in the desired purity by the cooling.Methionine with a purity of 80 to 100 wt. %, in particular 90 to 100 wt.%, which is not to be achieved in one-stage processes, is obtained withthis step of recrystallization.

The ration of amounts between the suspension pumped in circulation andthe solution admixed is in general 1-10:1, in particular 2-6:1,preferably 3-5:1.

The mixture claimed simplifies the process in the respect that duringthe precipitation of the methionine from the hydrolysis solution and therecrystallization of the methionine which has precipitated out, thissame mixture which comprises compound (1) and (2) can be employed.

However, the constituents (1) and (2) can also be added individually.(2) in particular displays its properties in particular during thecrystallization.

The invention is illustrated by the following examples.

EXAMPLE 1

Precipitation with Carbon Dioxide

A 4% emulsion of hydroxyethylcellulose, which has a viscosity of 200mPas (V=200) as a 2% solution, in water, and stearic acid ester 1 (n=17;m=7) in a weight ratio of 1:1 are introduced, while stirring, into 1 Lof a solution of potassium methioninate and potassium bicarbonate with amethionine concentration of 70 g/l and a potassium concentration of 150g/l, such that an emulsion which comprises 50 ppm of additives isformed. Carbon dioxide is fed in at pH=11 under a pressure of 2 bar in a2 L autoclave at a stirrer speed of 500 rpm. The addition of carbondioxide is continued at 30° C. until the pH is reduced to 8.0. Foamforms on the reaction mixture at a height of 1 centimeter, while at thesame time methionine is precipitated.

EXAMPLE 2

Recrystallization

60 g methionine are suspended at 40° C. in 300 ml water and 40 gfiltrate of the mother liquor from the precipitation with carbon dioxideand the suspension is pumped in circulation. A 4% emulsion ofhydroxyethylcellulose, which has a viscosity of 200 mPas (V=200) as a 2%solution, in water, and stearic acid ester 1 (n=18; m=7) in a weightratio of 1:1 are introduced, while stirring, into this suspension suchthat an emulsion which comprises 50 ppm of additives is formed. A heatexchanger is connected in series in order to keep the temperatureconstant. A hot solution at 90° C. of 180 g methionine in 1170 g waterand 150 g filtrate of the mother liquor from the precipitation withcarbon dioxide is added to this solution with a rate of 1 liter ofsolution per hour. The recrystallization of the methionine, which hasprecipitated out, in the presence of 50 ppm of the additives (totalamount), based on the methionine, leads to crystals with a bulk densityof 586 g/l.

The SEM photograph with the image number 173029 shows the coarselycrystalline structure of the end product obtained in this way.

Methionine precipitates out due to the cooling. 0.6 liter of the hotsolution is added, 500 ml of the circulating suspension are removed anda further 500 ml of hot solution are added. The suspension is filteredoff, the solid is rinsed with 300 ml acetone and dried to constantweight at 60° C. in a vacuum drying cabinet and the bulk density isdetermined.

A 4% emulsion of hydroxyethylcellulose, which has a viscosity of 200mPas (V=200) as a 2% solution, in water, and stearic acid ester 1 (n=18;m=7) in a weight ratio of 1:1 are introduced, while stirring, into thissolution which has been added dropwise, such that an emulsion whichcomprises 50 ppm of additives is formed.

EXAMPLE 3

Further Experiments

Further experiments which were carried out in accordance with Examples 1and 2 are summarized in Table 1. Deviating experimental conditions areto be found underneath the table. TABLE 1 Weight Foam Bulk Additive (2)Mixt ratio height density Experiment no.: Compound (1) (viscosity) (ppm)(1):(2) [cm] [g/l] 1 — — — — 15 420 2 n = 18; m = 7 — 160 — 1 470 3 —hydroxymethyl-  50 — 11 620 cellulose (200) 4 n = 18; m = 7hydroxymethyl-  50 1:1 1 586 cellulose (200) 5 n = 18; m = 7hydroxymethyl- 400 1:1 2 586 cellulose (300) 6 n = 18; m = 7hydroxymethyl- 400 2:1 2 571 cellulose (300) 7 n = 18; m = 7hydroxymethyl- 400 1:1 3 581 cellulose (300) 8 n = 18; m= 7hydroxymethyl-  50 1:1 3 572 cellulose (300) 9 n = 18; m = 7hydroxymethyl- 400 1:2 2 576 cellulose (300)Experiment 1: 71 g/l methionine and 175 g/l potassium in the solutionExperiment 8: Viscosity of additive 2 is 75-150 mPas at 25° C.Mixtures (ppm): Concentration of the mixture in the hydrolysis mixtureSEM photographs are attached for documentation of the advantageousresults which are achieved with this invention.

It is found that without the addition of additives (1) and (2), afine-particled methionine is obtained after the recrystallization (imageno.: 170867).

The use of compound (1), which in general has a defoaming action, alsoleads to no substantial coarsening of the crystal structure (image no.:170875).

The optimum results according to the invention are found only whenadditives (2) are employed together with (1) (image no.: 173029).

A comparison with image no. 173045 shows that the sole use of (2)already leads to results which exceed the prior art, but the addition of(1) has the effect of a further improvement. TABLE 2 Total amount ofBulk Image no.: Name/additive additives density Magnification 173029Additive (2) 50 ppm 586 g/l 100:1 (HEC) (n = 18, m = 7) 173045 Additive(2) 50 ppm 620 g/l 100:1 (HEC) 170875 Compound (1) 160 ppm  470 g/l100:1 (n = 18, m = 7) 170867 without (1) — 420 g/l 100:1 and (2)

1-13. (canceled)
 14. An aqueous mixture which comprises a compound ofthe formula:C_(n)H_(2n+x)C═O—O—(CH₂—CH₂—O)_(m)—H  (1), in which the symbols denote:n: an integer from 9 to 19, m: a distribution in the range from 1 to 10x: 1, −1, −3, −5, wherein 2n+x is not less than 1, and at least oneadditive which is a modified cellulose, in a weight ratio of 1:10 to10:1.
 15. The aqueous mixture according to claim 14, wherein n is 15, 17or
 19. 16. The aqueous mixture according to claim 14, wherein m is 5 to8.
 17. The aqueous mixture according to claim 16, wherein m is 6 or 7.18. The aqueous mixture according to claim 14, wherein the modifiedcellulose is a member selected from the group consisting ofmethylcellulose, methylhydroxycellulose, methylhydroxypropylcellulose,hydroxypropylcellulose, hydroxyethylcellulose, sodiumcarboxymethylcellulose, sodium carboxymethylhydroxyethylcellulose andsodium carboxymethylhydroxypropylcellulose in a weight ratio of 1:10 to10:1.
 19. The aqueous mixture according to claim 14, which has a totaladditive content of 1 to 5 wt. %, based on the total amount.
 20. Aprocess for the preparation of methionine comprising reacting a sourceof 3-methylmercaptopropionaldehyde, a source of hydrogen cyanide, asource of ammonia and a source of carbon dioxide, optionally in thepresence of water, to form 5-(2-methylmercaptoethyl)-hydantoin andconversion thereof into methionine, wherein, before carbon dioxide ispassed in, adding to a hydrolysis solution obtained from5-(2-methylmercaptoethyl)-hydantoin in a weight ratio of 1:10 to 10:1,an aqueous mixture which comprises a compound of the formula (1):C_(n)H_(2n+x)C═O—O—(CH₂—CH₂—O)_(m)—H(1), in which the symbols denote: n:a number from 9 to 19, m: a distribution in the range from 1 to 10, x:1, −1, −3, −5, wherein 2n+x is not less than 1, and an additive which isa modified cellulose, in particular methylcellulose,methylhydroxycellulose, methylhydroxypropylcellulose,hydroxypropylcellulose, hydroxyethylcellulose, sodiumcarboxymethylcellulose, sodium carboxymethylhydroxyethylcellulose andsodium carboxymethylhydroxypropylcellulose, in a total amount of 5 to5000 ppm based on the methionine contained in the solution, anddissolving methionine which has precipitated out and thenrecrystallizing to obtain the methionine.
 21. The process according toclaim 20, wherein m is 5 to
 8. 22. The process according to claim 20,wherein m is 6 or
 7. 23. The process according to claim 20, wherein theadditive is at least one member selected from the group consisting ofmethylcellulose, methylhydroxycellulose, methylhydroxypropylcellulose,hydroxypropylcellulose, hydroxyethylcellulose, sodiumcarboxymethylcellulose, sodium carboxymethylhydroxyethylcellulose andsodium carboxymethylhydroxypropylcellulose.
 24. The process according toclaim 20, wherein the weight ratio is 1:3 to 3:1.
 25. The processaccording to claim 20, wherein the total amount of 10 to 500 ppm. 26.The process according to claim 20, wherein recrystallizing is done usingcrystalline methionine suspended in mother liquor.
 27. The processaccording to claim 20, wherein compound (1) in which n corresponds to16, 18 or 20 is employed.
 28. The process according to claim 20, whereincompound (1) in which m is 5 to 8 is employed.
 29. The process accordingto claim 20, wherein compound (1) in which m is 6 or 7 is employed. 30.The process according to claim 20, wherein a compound (1) in which n=18and m=7 is employed.
 31. The process according to claim 20, whereinhydroxyethylcellulose is employed as additive.
 32. The process accordingto claim 20, wherein hydroxyethylcellulose which has a viscosity of 200mPas as a 1% solution is employed as additive.
 33. The process accordingto claim 20, wherein the aqueous mixture comprising (1) and the additiveis employed in the form of a pumpable emulsion in water.
 34. The processaccording to claim 20, wherein the aqueous mixture comprising (1) andthe additive is employed in the form of a 2-5% emulsion in water. 36.The process according to claim 20, wherein the aqueous mixturecomprising (1) and the additive is employed in a concentration of 10 to450 ppm of total additive concentration, based on methionineconcentration.
 37. The process according to claim 20, wherein during therecrystallizing, the aqueous mixture is added again in the desiredamount.